GB2371872A

GB2371872A - Vehicle data recorder with varying recording density

Info

Publication number: GB2371872A
Application number: GB0122613A
Authority: GB
Inventors: Markus Klausner; Georg Pfaff
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2000-09-21
Filing date: 2001-09-19
Publication date: 2002-08-07
Anticipated expiration: 2021-09-19
Also published as: DE10046696A1; US6629030B2; GB0122613D0; GB2371872B; JP2002183876A; US20020107619A1

Abstract

A data recorder determines vehicle parameter values and records data relating to these values, the data being suitable for the reconstruction of vehicle accidents The resolution with which the data is recorded varies with the time interval between parameter determination time t and the current time t<SB>u</SB>. A method and device are disclosed where the values are recorded with decreasing density as the time interval between the parameter determination time and the current time increases, thus the 'older' less recently determined data values are recorded with less resolution than newly determined values. This allows all relevant data to be recorded continuously with a low storage capacity. The recorded data may quickly be permanently stored by parallel transfer to a non-volatile memory when an accident is detected. A storage module having a RAM is also disclosed, as is the use of an ASIC.

Description

Method and Device for Recording Vehicle Data Prior art

5 The present invention relates to a method and to a device for recording data from parameter values acquired or determined, in particular by means of sensors, in a vehicle, in particular for the reconstruction of accidents, as well as to a storage module for recording such data, according 10 to the precharacterising clauses of the independent claims.

EP 0 078 807 B1 discloses, in order to ascertain the cause of accident in the case of vehicles with an anti-lock system (ABS), the storage of driving condition values, such as vehicle speed, braking distance and deceleration, which 15 are acquired by means of sensors and can be calculated, in order to reconstruct the accident therefrom, since vehicles with ABS do not usually leave clear skid-marks.

Accident data recorders are discussed in an article from Wirtschaftswoche [Business Week] No 10, pp. 60 to 62, of 20 3.3.1989 ("Black Box im Auto" [Black box in the car]). The accident data recorder is supplied by sensors which pick up all the changes in the car's movement. Further data (light or indicator switch setting, steering, pedal and clutch movements, etc.) can be registered. All the data is stored 25 on a chip and overwritten every 30 seconds by current data.

The chip content is frozen in the event of an accident, further data being recorded until the car comes to a stop.

Lastly, an accident data recorder and a method for analysing an accident event are known from DE 195 09 711 Al.

An attempt is made therein to reduce the high inaccuracy when establishing the accident data (speed and braking distance) by employing GPS signals (Global Positioning System), in addition to the data from an accident data 5 recorder, for the evaluation. Sufficiently exact relative positioning can be carried out by means of this, the absolute positioning (zero offset correction) being performed by the known accident data recorder. This document mentions the problem that, for sufficiently 10 accurate calculation of the accident data by means of a conventional accident data recorder, a separate sensor would be required for each of the three translational and three rotational degrees of freedom of the vehicle movement, which would entail unacceptable outlay in terms of 15 computing and sensor technology.

In fact, conclusions about the vehicle dynamics during an

accident (usually related to abrupt braking, skidding or impact) require parameter acquisition at an interval of, for example, 20 - 40 ms, and even less than 20 ms for 20 individual parameters such as the wheel speed. If it is assumed that 70 parameters for accident reconstruction are picked up every 20 ms with a width of 2 bytes over a period of 30 seconds, 205 Kbytes of storage would be required.

The method described in DE 195 09 711 Al for accident 25 reconstruction, with the incorporation of GPS signals, requires a corresponding reception system and likewise considerable outlay in terms of computing technology.

Furthermore, the retrofitting of existing systems proves difficult. 30 A further disadvantage of known accident data recorders is the long time taken to transfer the data recorded in the volatile memory (RAM) to a nonvolatile memory (e.g. EEROM).

J The RAM content is typically written to an EEPROM via a serial bus such as SPI. The transfer time increases linearly with the number of bytes to be transferred. The slow transfer rate (e.g. 10 ms/byte), for transferring the 5 required data volume after an impact with probable loss of the supply voltage due to damage of components in the vehicle electrical system or defined battery switch-off after accident detection, is unsuitable for implementing an accident data storage functionality.

10 Accident data recorders are also known in which the corresponding data is not transferred from a RAM to an EEPROM. For example, it is possible to design the REM with battery buffering, this embodiment being known in the case of at least one commercially available accident data 15 recorder. Battery buffering, however, is considered to be very unfavourable in control units, since they do not have their own batteries and the vehicle electrical system can fail in the event of an accident. As already mentioned, however, a serial bus is often used when data needs to be 20 transferred, in control units, from a RAM to an EEPROM.

Advantages of the Invention It is an object of the present invention to provide a method and a device for recording data from parameter values acquired by means of sensors in a vehicle, in 25 particular for the reconstruction of accidents, as well as a storage module for recording such data, with the aim of allowing all relevant data to be recorded continuously with a low storage capacity and to be saved permanently in a short length of time.

This object is achieved according to the invention by the features of the independent claims. Advantageous configurations can be found in the description and the

dependent claims. A suitable embodiment is specified in S Claim 7.

The invention furthermore relates to a computer program on a storage medium, or data carrier, which, when it is executed on a computer or a control unit, performs a method according to the invention. The relevant storage medium may 10 in this case be permanently integrated in the computer, or the control unit, such as e.g. a RAM, E(E)PROM, flash EPROM, a hard disk, etc., or alternatively mobile, such as e.g. a floppy disk, a CD-ROM or the like.

According to the invention, the parameter values and/or 15 data calculated from them are recorded with decreasing density as the chronological separation from the current acquisition time increases. This is because it has been shown that a high recording density is required only in a very short period before an accident, since high rates of 20 change of the parameter values are then probable. Less recent values can be recorded with lower resolution, since smaller rates of change can be assumed and the relevance of the information decreases as the chronological separation from the accident increases.

25 The recording density can, according to the invention, decrease e.g. exponentially, linearly or in steps as the chronological separation from the current acquisition time (i.e. from the possible accident time) increases. It is advantageous, and straightforward to implement in practical 30 terms, for the parameter values to be recorded with discretely decreasing recording frequency, a suitable

predeterminable number of steps (for example from 2 to 8, advantageously from 3 to 6) being set over the recording period. In a particular version of the method according to the 5 invention, representative data, such as extreme or mean values are calculated from the acquired parameter values, and are recorded. This is advantageous, in particular, if the data is recorded with a very low recording frequency.

It is then possible to compensate partially for the 10 information lost owing to the large separation of the recording times. For example, the minimum value, the maximum value and the mean value of a parameter between two recording times can be calculated and stored. Important information can be obtained in this way, although fewer 15 values can be recorded than at the maximum recording frequency. The method according to the invention can be used not only to reconstruct vehicle accidents by means of the recorded data, but also, for example, to evaluate parts stress, to 20 ascertain service life and/or wear on individual parts etc., so long as the parameters needed for this are measured by means of suitable sensors or otherwise determined. The recording period and the profile of the recording frequency need to be fixed for the respective application and the 25 respective parameters. The data could, for example, be evaluated in relation to the time when the replacement of a spare part is indicated owing to previous stress.

For accident reconstruction, it is advantageous for the recorded data to be transferred in parallel to a non 30 volatile memory after a vehicle accident. The transfer duration then no longer grows linearly with the data volume

but, rather, immediate storage after an accident or a defined event is possible.

The invention furthermore provides a storage module for recording data from parameter values acquired by means of 5 sensors in a vehicle, in particular for the reconstruction of vehicle accidents, use being made of a RAM (Random Access Memory) for recording the data respectively over a specific period and a non-volatile memory, to which the recorded data can be transferred in parallel from the RAM.

10 An accident can be identified in various ways. Either the vehicle electrical system fails through damage to the components, or the accident is detected using sensors, special detection algorithms being employed for this. Such a situation requires non-volatile saving of the recorded 15 data volume in the shortest possible time. In other applications as well, permanent saving of the recorded data immediately after a defined event may be desirable.

To that end, according to the invention, a so-called nvSRAM (non-volatile Static Random Access Memory) is used. The 20 S RAM replaces the RAM in normal operation and is connected in parallel to a non-volatile memory (such as EEPROM). The circuit is organised so that, when the supply voltage drops below a defined threshold value or when a defined event occurs, the entire S RAM content is permanently stored in 25 less than 10 ma.

As an alternative, it is possible to employ any other storage technology which permits the non-volatile storage of large data volumes, e.g. several kilobytes (Kbytes), in a short time, e.g. in a few milliseconds (ms). Examples of

this include FeRAM (ferroelectric RAM) and flash banks (flash memories).

For implementing the accident data storage functionality in a vehicle, the use of an ASIC (Application Specific 5 Integrated Circuit) in the control unit of the vehicle is particularly suitable. Many sensors do not communicate with the vehicle bus, but instead are connected to the control unit (directly or via a field bus). In this case, the

control unit makes sensor information available via the bus.

10 By means of this, it is possible to make optimum use of structures which are present in any case. The data delivered by the sensors is further utilised for the accident reconstruction, the sensor data being available via the vehicle bus (e.g. CAN) and the desired data being 15 evaluated by means of software. An ASIC is advantageous, in particular, when an nvSRAM is used for data storage. It is merely necessary to equip the control unit with the ASIC without further hardware modifications, and the required software modifications are minimized. Selective upgrading 20 with the accident data storage functionality is possible.

Further advantages and advantageous configurations can be found in the description and the claims.

Drawing The invention will be explained in more detail below, with 25 the aid of the appended figures contained in the drawing, by exemplary embodiments represented in the drawing.

Figure 1 shows a first function 1 according to the invention for the reduction of the recording density of a parameter value as the chronological separation from the 30 current acquisition time increases.

Flqure 2 shows a second function 2 according to the invention for the reduction of the recording density of a parameter value as the chronological separation from the current acquisition time increases.

5 Figure 3 shows the basic structure of an ASIC 8 with an nvSRAM 7 being used for data storage for the accident reconstruction. In Figure 1, the recording period is denoted by T. T lies in the region of e.g. 60 seconds, it being expedient, for 10 accident reconstruction after crash detection, to continue picking up data for a further time, e.g. approximately 5 to 10 seconds, before the entire memory content is permanently stored, if this is possible according to the situation or the accident profile. Depending on requirements, longer or 15 shorter lengths of recording time are conceivable The recording density is reduced according to the invention as the chronological separation from the accident time tu increases. The function 1 shows a non-linear, substantially exponential profile, which represents continuous data 20 compression.

The function 2 represented in Figure 2 describes a multi-

step, here three-step, reduction of the recording density.

The recording frequency up to the time t1 before the accident time to is f1 [s-1], before which it is f2 up to the 25 time t2, and then only f3 up to the time t3. The constants f1, f2, f3, t: and t2 are respectively to be fixed parameter-

specifically or, alternatively, arbitrarily gettable.

The saving E on the RAM needed for the parameter recording and on the nonvolatile memory, compared to an invariant 30 recording density, can be calculated as follows:

E = 1 - f '(t' - tu) + f 2(t - tt) + f 3(ti - t2) f,(t;-to) This formula (I) can be extended analogously for any desired number of steps.

In a particular type of embodiment, for the period t3 to t2, 5 parameter values calculated from a plurality of intermediate values are recorded at each recording time, although fewer values overall than when a recording frequency f2 is used. For example, the minimum value, the maximum value and the average value of the parameter 10 between two recording times are stored. In this way, it is possible to compensate at least in part for the information lost because of the lower recording frequency. This is particularly useful when fl is very small, edgy f1 corresponds to 1 Hz. If b calculated values of a parameter 15 are recorded at each recording time (in the above example, b=3) in the period t2 to t3, then the memory saving Eb is now according to formula (II) below: Eb = 1 _ f l(t' - tU) + f 2(t2 - tI) + bf 3(t3 - t,) f '(t3-tU) For typical practical applications, memory savings of 80 20 90\ can be achieved.

Figure 3 schematically represents the structure of an ASIC 8 for implementing the accident data storage functionality in a motor vehicle control unit. Sensors (not shown) forward their signals via the motor vehicle bus 3

(e.g. CAN) to corresponding reception u- ts, such as the control unit. To that end, the microprc essor 5 of the ASIC, which communicates via the bus controller with the motor vehicle bus 3, is connected to the micrcorocessor 6 of the 5 control unit. At this point, it should He mentioned that the ASIC does not need to be provided w oh its own bus controller. Nevertheless, the use of a separate bus controller is advantageous whenever the signals needed by the bus are different from the signals Deeded by the 10 control unit, in which the ASIC is intec- ated. According to the invention, an nvSRAM 7 is provided, which records the parameter values relevant to the accident reconstruction, in particular by means of the recording method according to the invention, and permanently stores them within a few ms 15 in the event of an accident. To that end, it is not necessary to resort to discrete energy stores, such as capacitors in the control unit.

A wealth of advantages compared to known accident data recorders can be achieved by combining the ASIC 8 20 represented in Figure 3, with the use of the nvSRAM 7, and a recording density function according to the invention.

The need for RAM and non-volatile memory (e.g. flash EEPROM) is reduced significantly compared to the known ring storage principle with fixed recording frequency. The hardware 25 costs are thereby lowered. The described method makes it possible to acquire a long history before the accident with increasing accuracy.

The problem of transferring the entire RAM content to the non-volatile memory after loss of the supply voltage is 30 solved by the invention. In contrast to the known methods, the entire data record is written in parallel, e.g. to an

EEPROM, in only a few ms, and the need to use discrete capacitors as energy stores in the control unit is obviated.

Another advantage is that, owing to the use of an ASIC, no modifications to the hardware needed for fulfilling the 5 control unit function are required. The software modifications are minimized. The ASIC permits selective implementation of the accident data storage functionality by equipping the control unit with the ASIC.

The subject-matter of the invention is not, however, 10 limited to the examples which have been mentioned.

Comparable solutions are likewise subsumed under the basic principle of the invention, namely that of data recording with variable density matched to the chronological separation from the accident time.

Claims

Claims 1. Method for recording data from parameter values 5 acquired or

determined in a vehicle, characterized in that the parameter values and/or data calculated from them are recorded with decreasing density as the chronological separation from the current acquisition or determination time increases.

10 2. Method according to Claim 1, characterized in that the parameter values Are recorded with discretely decreasing recording frequency (f1, f2, f3, etc.).

3. Method according to Claim 1 or 2, characterized in that representative data, such as extreme or mean values, 15 -in particular for recording intervals with low recording frequency, are calculated from the acquired parameter values and are recorded.

4. Use of the method according to one of Claims 1 to 3 for the reconstruction of vehicle accidents by means of the 20 recorded data.

5. Method according to Claim 4, characterized in that the recorded data is transferred in parallel to a non-volatile memory after a vehicle accident.

6. Storage module for recording data from parameter 25 values acquired or determined in a vehicle, in particular for the reconstruction of vehicle accidents, characterized by a first storage medium, in particular a RAM (Random Access Memory), for recording the data respectively over a

specific period and by a second non-volatile storage medium, to which the recorded data can be transferred in parallel from the first storage medium, or other suitable storage technology media which permit the nonvolatile saving of 5 data volumes, in particular several Kbytes, in a short time, in particular a few ms, the recording density being variable as a function of the acquisition or determination time. 7. Use of an ASIC (8) (Application Specific Integrated 10 Circuit) in the control unit of a vehicle for recording data from parameter values, acquired by means of sensors in a vehicle, for the reconstruction of accidents, in particular with an integrated storage module according to Claim 6.

15 8. Device for recording data from parameter values acquired or determined in a vehicle, in particular for the .. reconstruction of vehicle accidents, which contains at least one storage medium, characterized in that means are contained which record the parameter values and/or data 20 calculated from them with decreasing density as the chronological separation from the current acquisition or determination time increases.

9. Computer program on a storage medium, through which, when run on a computer, in particular a control unit, a 25 method according to at least one of Claims 1 to 5 can be carried out.: 10. Method for recording data substantially as hereinbefore described with reference to the accompanying drawings.

11. Storage module substantially as hereinbefore described with reference to the accompanying drawings 12. Device for recording data substantially as 5 hereinbefore described with reference to the accompanying drawings. 13. Computer program according to claim 9 as substantially as hereinbefore described with reference to the 10 accompanying drawings.